1. Field of the Invention
The present invention relates to displaying landscape mode images. More particularly, embodiments of the invention relate to a method of effectively managing the display of a landscape mode image utilizing a timing controller and a mobile liquid crystal display (LCD) device.
2. Discussion of Related Art
Liquid crystal display (LCD) devices have been utilized in desktop computers and mobile devices such as cellular phones and palmtop computers. LCDs used in mobile devices (hereinafter referred to as a “mobile LCD device”) have low manufacturing costs and require low power consumption. Mobile LCD devices are also designed to optimize the display of a portrait mode image rather than a landscape mode image.
FIG. 1 is a timing diagram illustrating a set of signals used when a conventional mobile LCD device displays a single video frame. A set of signals needed when a single video frame is displayed includes a vertical synchronization signal VSYNC, a horizontal synchronization signal HSYNC and a data enable signal DE. The vertical synchronization signal VSYNC 110 is used for representing a starting point of the single video frame. The mobile LCD device displays the single video frame when the vertical synchronization signal VSYNC is active. Horizontal synchronization signal HSYNC 120 is used for representing a starting point of a single horizontal line of the single video frame. The mobile LCD device displays the single horizontal line when the horizontal synchronization signal HSYNC is active. When the vertical synchronization signal VSYNC 110 is generated once, a plurality of horizontal synchronization signals HSYNCs are generated. Data enable signal DE 130 is used for representing a starting point of data transmission in the single horizontal line. Data corresponding to the single horizontal line is transmitted to the mobile LCD when the data enable signal DE is active.
FIG. 2 is a diagram for illustrating a procedure where a video frame is read from or written to a video memory when a mobile LCD device displays a landscape mode image. First, when a portrait mode image is written into video memory 210, the image is written in horizontal direction 230. When a landscape mode image is written into video memory 210, the image is written in a vertical direction 220. This is because the mobile LCD device is optimized for supporting the portrait mode. When the portrait mode image is read from video memory 210, the image is read in a horizontal direction 230. Similarly, when the landscape mode image is read from video memory 210, the image is also read in horizontal direction 230. Thus, the mobile LCD device reads the video frame in a horizontal direction 230 from video memory 210 regardless of whether the image mode is portrait or landscape.
FIG. 3 is a timing diagram illustrating a set of signals used when a conventional mobile LCD device displays a landscape mode image. A set of signals used when the mobile LCD device displays a landscape mode image includes a vertical synchronization signal VSYNC 310, an external data enable signal EXTERNAL_DE 320, an internal data enable signal INTERNAL_DE 330, a display output signal DO 340 and a common voltage signal VCOM 350. Vertical synchronization signal VSYNC 310 is used for representing a starting point of a single video frame. The mobile LCD device displays the single video frame when the vertical synchronization signal VSYNC is active. For example, the mobile LCD device may receive 60 vertical synchronization signals VSYNCs per second. A horizontal synchronization signal HSYNC (not illustrated) is used for representing a starting point of a single horizontal line of the single video frame. The mobile LCD device displays the single horizontal line when the horizontal synchronization signal HSYNC is active. When the vertical synchronization signal VSYNC 310 is generated once, a plurality of horizontal synchronization signals HSYNCs are generated.
External data enable signal EXTERNAL_DE 320 is used for representing a starting point of data transmission in the single horizontal line. Data corresponding to the single horizontal line is transmitted to the mobile LCD device when the external data enable signal EXTERNAL_DE is active. Internal data enable signal INTERNAL_DE 330 is used for representing a starting point of data storage in the single horizontal line. The data is stored into the video memory when the internal data enable signal INTERNAL_DE 330 is active. For example, when four external data enable signals EXTERNAL_DEs are generated, one internal data enable signal INTERNAL_DE may be generated. That is, the mobile LCD device receives the four frame data and may select one of the four frame data to store the selected one. Display output signal DO 340 represents a starting point of outputting of the video frame. The video frame is read from the video memory when the display output signal DO 340 is active. However, display output signal DO 340 is masked when internal data enable signal INTERNAL_DE 320 is active. Common voltage signal VCOM 350 is used for updating a display in the mobile LCD device. The mobile LCD device displays the video frame when the common voltage signal VCOM 350 is changed from a high voltage to a low voltage or from a low voltage to a high voltage.
In general, a period of common voltage signal VCOM 350 is equal to that of display output signal DO 340. Common voltage signal VCOM 350 is changed 80 times per second in order for the mobile LCD device to display 60 video frames per second. This is because the video frame is masked when internal data enable signal INTERNAL_DE 330 is active. However, if common voltage signal VCOM 350 is changed while internal data enable signal INTERNAL_DE 320 is active, a display problem in the mobile LCD device occurs.
FIGS. 4A, 4B and 4C are diagrams illustrating such a problem when a conventional mobile LCD device displays a landscape mode image. FIG. 4A represents an original video frame stored in the mobile LCD device. FIGS. 4B and 4C represent video frames that may occur if common voltage signal VCOM 350 is changed while internal data enable signal INTERNAL_DE 330 is active. The noise illustrated in FIGS. 4B and 4C occurs because the direction in which the video frame is written into the video memory is not the same as the direction in which the video frame is read from the video memory. Accordingly, there is a need for providing an LCD device for effectively displaying a landscape mode image.